In the past, various products made of iron, stainless steel, copper, or other metals plated with another metal have been produced. As the products, auto parts, for example, engine parts, electrical and electronic parts, etc. may be mentioned. As the type of plating, zinc plating, nickel plating, copper plating, tin plating, zinc-nickel alloy plating, etc. may be mentioned.
As the system of plating of such products, the immersion system is most generally used. The immersion system is a system where a workpiece made of a metal is immersed as a cathode in a plating tank containing a plating solution and is electrode-reacted with an anode facing the cathode.
The immersion system of plating treatment had the problems accompanying so-called batch processing. That is, for example, as shown in FIG. 1, in pretreatment for hot dip zinc coating, the steps of degreasing, rinsing, pickling, rinsing, and flux treatment became necessary. A separate treatment tank had to be prepared for each of these steps and, with the end of each step, the workpiece had to be conveyed to the next treatment tank. For this reason, the plating facility became extremely large in size. Along with the larger size of the facility, a conveyance apparatus also became necessary. Therefore, there was the problem that the facility easily became higher in cost.
To solve this problem, in, for example, PLT 1, a continuous type chemical surface treatment apparatus comprised of a single work tank and a plurality of storage tanks has been proposed.
However, when providing, for example, a solenoid valve or other mechanism for switching solutions at the outside of a treatment tank, the piping from the switching mechanism to the treatment tank is used in common for the different treatment solutions. An amount of each treatment solution equal to the common piping has to be discharged in order to prevent intermixture, so the amounts of use of the solutions increase.